i) Field of the invention
The present invention relates to a heat insulating box structure and a manufacturing method therefor, and, more particularly, to a heat insulating box structure filled with foam heat-insulating material in a gap between the inner and the outer boxes thereof and a manufacturing method therefor.
ii) Description of the prior art
A heat insulating box structure disclosed in Japanese Patent Laid-Open No. 61-173068 is constituted in such a manner that a heat insulating and flexible pipe is fastened along the inner surface of the outer box, the heat insulating and flexible pipe having an end portion positioned in the vicinity of an injection port (or a pour hole) formed in the outer box and another end portion positioned in the vicinity of a position where foam solution is injected through the above-described injection port. The pipe is arranged in a zigzag manner so that the foam solution injected through the injection port passes through the thus arranged zigzag pipe.
According to the above-described conventional structure, the pipe is arranged in such a manner that an end portion thereof is positioned in the vicinity of the injection port formed in the outer box and another end portion is positioned in the vicinity of the position where the foam solution is injected. However, it is difficult for the foam solution to foam uniformly in the overall body of a heat insulating box structure having two storage areas disposed close to each other and arranged such that the foam solution is injected into the space formed between the inner box and the outer box thereof. Thus, a problem arises in that portions which are not filled with the foam solution occur and residual air is thereby generated. What is worse, the distribution of the enclosed heat insulating material is not uniform.
On the other hand, even if the quantity of the foam solution to be injected is increased for the purpose of eliminating the portions which are not filled with the foam solution, the difficulty of distributing the increased amount of foam solution cannot be overcome. Thus, a problem arises in that the heat insulating material distribution cannot be uniform in the overall body of the heat insulating box structure. It might therefore be feasible to employ a structure in which other injection ports are formed in other surfaces in addition to the above-described surface so that a plurality of the storage areas are independently supplied with the foam solution. However, a problem arises in that the injection operation becomes too complicated since a plurality of injection guns must be used or the heat insulating box structure must be turned so as to fill it with the foam solution.